The war on terror after 2001 caused many changes and one of the less well-known ones was the large number of new weapons designs that appeared. One of the more interesting, but generally unnoticed areas of developments is the PDW (Personal Defense Weapon, or pistol replacement). A recent design shows how compact and lightweight a powerful machine pistol can be. The Russian PP-2000 PDW uses 9x19mm round (the most widely used pistol round ever). The PP-2200 weighs 1.4 kg (3.1 pounds) has a 183mm (7.2 inch) long barrel and can use 20 or 40 round double stack (short) magazines. It has a folding stock so it can be used like a pistol or a submachinegun. You can attach a red dot sight and light (to the bottom). When folded up in “pistol” mode it will fit in a jacket.
In the West there has also been a lot of PDW work. In 2010 for example the Rock River Arms PPS (Performance Piston System) Pistol appeared. This is a 5.56mm weapon that uses a new internal design. It has a short gas piston, with the recoil spring and guide rod over the 21cm (8 inch) barrel. The entire weapon (which does not have a stock) is 44.5cm (17.5 inches) long and weighs 2.2 kg (5 pounds). There are single shot and full automatic versions, each costing $1,335. There have been some notable European PDW designs from the major pistol manufacturers like H&K.
If you want a smaller PDW, you often have to go with smaller ammunition. An example of this is a recent Chinese PDW design that uses a 4.6x30mm round. This weapon is a variant of the Type 79 PDW which uses the old Russian 7.62x25mm round. The new Chinese weapon weighs 1.6 kg (3.6 pounds) and has a 30 round, dual stack, magazine. Rate of fire is single, 400 or 600 rounds per minute. It has a Picatinny rail on top for scopes and sights. With the telescopic stock closed, the weapon is 34cm (13.4 inches) long, and 54cm (21.2 inches) with the stock extended. The weapon is gas operated with a closed bolt. The bullets are about half the weight of 5.56mm ones and the 4.6mm round is lethal at short ranges, especially in bursts. The bullet travels at high speed (over 700 meters a second). The 4.6mm round will not penetrate walls or ceilings as well as 9mm or 5.56mm bullets, meaning less chance of unintended casualties.
The Personal Defense Weapon never really succeeded, on a large scale, as a pistol replacement. The military, especially in the United States, simply developed an M-16 with a shorter barrel and stock (the M-4). Many troops who previously only had a pistol, now had an M-4. These were cheaper than PDWs, and not much larger. But security professionals, especially bodyguards, are a growing market for the easily concealed PDWs. Some police departments use them.